1,008 research outputs found
Imaging the Small-Scale Circumstellar Gas Around T~Tauri Stars
We have detected circumstellar molecular gas around a small sample of T Tauri
stars through aperture synthesis imaging of CO(2-1) emission at ~2-3''
resolution. RY Tauri, DL Tauri, DO Tauri, and AS 209 show resolved and
elongated gaseous emission. For RY Tau, the deconvolved, half-maximum radius
along the direction of elongation, PA~48deg, is 110 AU. Corresponding radii and
orientations for the other sources are: DL Tau -- 250 AU at PA~84deg; DO Tau --
350 AU at PA~160deg; AS 209 -- 290 AU at PA~138deg. RY Tau, DL Tau, and AS 209
show velocity gradients parallel to the elongation, suggesting that the
circumstellar material is rotating. RY Tau and AS 209 also exhibit
double-peaked spectra characteristic of a rotating disk. Line emission from DO
Tau is dominated by high-velocity blue-shifted gas which complicates the
interpretation. Nevertheless, there is in each case sufficient evidence to
speculate that the circumstellar emission may arise from a protoplanetary disk
similar to that from which our solar system formed.Comment: TeX file with associated macros, no figures; AJ in press. Also
available as a compressed postscript file (including figures) by anonymous
ftp at ftp://cougar.jpl.nasa.gov/pub/davidk/preprints/COinTTS.ps.
Keck Imaging of Binary L Dwarfs
We present Keck near-infrared imaging of three binary L dwarf systems, all of
which are likely to be sub-stellar. Two are lithium dwarfs, and a third
exhibits an L7 spectral type, making it the coolest binary known to date. All
have component flux ratios near 1 and projected physical separations between 5
and 10 AU, assuming distances of 18 to 26 pc from recent measurements of
trigonometric parallax. These surprisingly similar binaries represent the sole
detections of companions in ten L dwarf systems which were analyzed in the
preliminary phase of a much larger dual-epoch imaging survey. The detection
rate prompts us to speculate that binary companions to L dwarfs are common,
that similar-mass systems predominate, and that their distribution peaks at
radial distances in accord both with M dwarf binaries and with the radial
location of Jovian planets in our own solar system. To fully establish these
conjectures against doubts raised by biases inherent in this small preliminary
survey, however, will require quantitative analysis of a larger volume-limited
sample which has been observed with high resolution and dynamic range.Comment: LaTex manuscript in 13 pages, 3 postscript figures, Accepted for
publication in the Letters of the Astrophysical Journal; Postscript pre-print
version available at: http://www.hep.upenn.edu/PORG/papers/koerner99a.p
Imaging the Haro 6-10 Infrared Companion
We present an infrared imaging study of the low-mass pre-main-sequence binary system Haro 6-10. This system is one of a handful in which the optically visible primary has the characteristics of a normal T Tauri star, while the secondary is a so-called "infrared companion" (IRC), a strongly extincted object that emits most of its luminosity in the infrared. A speckle holographic technique was used to produce nearly diffraction-limited images on three nights over a 1 yr period starting in late 1997. The images show that the IRC is obscured and surrounded by a compact, irregular, and variable nebula. This structure is in striking contrast to the well-ordered edge-on disk associated with HK Tauri B, the extincted companion to another T Tauri star of similar age. A new, resolved intensity peak was found 0".4 southwest of the IRC. We suggest that it may represent light scattered by a clump of dusty material illuminated by starlight escaping along an outflow-carved cavity in the IRC envelope. The primary star became fainter and the companion became more extended during the observing period
Mid-infrared Imaging of a Circumstellar Disk Around HR 4796: Mapping the Debris of Planetary Formation
We report the discovery of a circumstellar disk around the young A0 star, HR
4796, in thermal infrared imaging carried out at the W.M. Keck Observatory. By
fitting a model of the emission from a flat dusty disk to an image at
lambda=20.8 microns, we derive a disk inclination, i = 72 +6/-9 deg from face
on, with the long axis of emission at PA 28 +/-6 deg. The intensity of emission
does not decrease with radius as expected for circumstellar disks but increases
outward from the star, peaking near both ends of the elongated structure. We
simulate this appearance by varying the inner radius in our model and find an
inner hole in the disk with radius R_in = 55+/-15 AU. This value corresponds to
the radial distance of our own Kuiper belt and may suggest a source of dust in
the collision of cometesimals. By contrast with the appearance at 20.8 microns,
excess emission at lambda = 12.5 microns is faint and concentrated at the
stellar position. Similar emission is also detected at 20.8 microns in residual
subtraction of the best-fit model from the image. The intensity and ratio of
flux densities at the two wavelengths could be accounted for by a tenuous dust
component that is confined within a few AU of the star with mean temperature of
a few hundred degrees K, similar to that of zodiacal dust in our own solar
system. The morphology of dust emission from HR 4796 (age 10 Myr) suggests that
its disk is in a transitional planet-forming stage, between that of massive
gaseous proto-stellar disks and more tenuous debris disks such as the one
detected around Vega.Comment: 9 pages, 4 figures as LaTex manuscript and postscript files in
gzipped tar file. Accepted for publication in Astrophysical Journal Letters.
http://upenn5.hep.upenn.edu/~davidk/hr4796.htm
The Inner Rings of Beta Pictoris
We present Keck images of the dust disk around Beta Pictoris at 17.9 microns
that reveal new structure in its morphology. Within 1" (19 AU) of the star, the
long axis of the dust emission is rotated by more than 10 degrees with respect
to that of the overall disk. This angular offset is more pronounced than the
warp detected at 3.5" by HST, and in the opposite direction. By contrast, the
long axis of the emission contours at ~ 1.5" from the star is aligned with the
HST warp. Emission peaks between 1.5" and 4" from the star hint at the presence
of rings similar to those observed in the outer disk at ~ 25" with HST/STIS. A
deconvolved image strongly suggests that the newly detected features arise from
a system of four non-coplanar rings. Bayesian estimates based on the primary
image lead to ring radii of 14+/-1 AU, 28+/-3 AU, 52+/-2 AU and 82+/-2 AU, with
orbital inclinations that alternate in orientation relative to the overall disk
and decrease in magnitude with increasing radius. We believe these new results
make a strong case for the existence of a nascent planetary system around Beta
Pic.Comment: 5 pages, 2 figures, PDF format. Published in ApJL, December 20,200
A Pulsed Eddy Current Method for Examining Thin-Walled Stainless Steel Tubing
A bellows is fabricated from a 12-in. section of type 321 or type 216 stainless steel tubing. In order to ensure that the bellows will survive the rigors of the production environment, it is essential that the tubing be free of all “scratch like” defects. A feasibility study was conducted to determine if an eddy current method could be developed to nondestructively examine this tubing
Millimeter-Wave Aperture Synthesis Imaging of Vega: Evidence for a Ring Arc at 95 AU
We present the first millimeter-wave aperture synthesis map of dust around a
main sequence star. A 3'' resolution image of 1.3 mm continuum emission from
Vega reveals a clump of emission 12'' from the star at PA 45 deg, consistent
with the location of maximum 850 micron emission in a lower resolution
JCMT/SCUBA map. The flux density is 4.0+/-0.9 mJy. Adjacent 1.3 mm peaks with
flux densities 3.4+/-1.0 mJy and 2.8+/-0.9 mJy are located 14'' and 13'' from
the star at PA 67 deg and 18 deg, respectively. An arc-like bridge connects the
two strongest peaks. There is an additional 2.4 +/-0.8 mJy peak to the SW 11''
from the star at PA 215 deg and a marginal detection, 1.4+/-0.5 mJy, at the
stellar position, consistent with photospheric emission. An extrapolation from
the 850 micron flux, assuming F_{1.3mm-0.85mm} proportional to lambda^{-2.8},
agrees well with the total detected flux for Vega at 1.3 mm, and implies a dust
emissivity index, beta, of 0.8. We conclude that we have detected all but a
very small fraction of the dust imaged by SCUBA in our aperture synthesis map
and that these grains are largely confined to segments of a ring of radius 95
AU.Comment: 4 pages, 1 figure, 1 table, accepted for publication in Astrophysical
Journal Letter
Radial Distribution of Dust Grains Around HR 4796A
We present high-dynamic-range images of circumstellar dust around HR 4796A
that were obtained with MIRLIN at the Keck II telescope at lambda = 7.9, 10.3,
12.5 and 24.5 um. We also present a new continuum measurement at 350 um
obtained at the Caltech Submillimeter Observatory. Emission is resolved in Keck
images at 12.5 and 24.5 um with PSF FWHM's of 0.37" and 0.55", respectively,
and confirms the presence of an outer ring centered at 70 AU. Unresolved excess
infrared emission is also detected at the stellar position and must originate
well within 13 AU of the star. A model of dust emission fit to flux densities
at 12.5, 20.8, and 24.5 um indicates dust grains are located 4(+3/-2) AU from
the star with effective size, 28+/-6 um, and an associated temperature of
260+/-40 K.
We simulate all extant data with a simple model of exozodiacal dust and an
outer exo-Kuiper ring. A two-component outer ring is necessary to fit both Keck
thermal infrared and HST scattered-light images. Bayesian parameter estimates
yield a total cross-sectional area of 0.055 AU^2 for grains roughly 4 AU from
the star and an outer-dust disk composed of a narrow large-grain ring embedded
within a wider ring of smaller grains. The narrow ring is 14+/-1 AU wide with
inner radius 66+/-1 AU and total cross-sectional area 245 AU^2. The outer ring
is 80+/-15 AU wide with inner radius 45+/-5 AU and total cross-sectional area
90 AU^2. Dust grains in the narrow ring are about 10 times larger and have
lower albedos than those in the wider ring. These properties are consistent
with a picture in which radiation pressure dominates the dispersal of an
exo-Kuiper belt.Comment: Accepted by Astrophysical Journal (Part1) on September 9, 2004. 13
pages, 10 figures, 2 table
A Single Circumbinary Disk in the HD 98800 Quadruple System
We present sub-arcsecond thermal infrared imaging of HD 98800, a young
quadruple system composed of a pair of low-mass spectroscopic binaries
separated by 0.8'' (38 AU), each with a K-dwarf primary. Images at wavelengths
ranging from 5 to 24.5 microns show unequivocally that the optically fainter
binary, HD 98800B, is the sole source of a comparatively large infrared excess
upon which a silicate emission feature is superposed. The excess is detected
only at wavelengths of 7.9 microns and longer, peaks at 25 microns, and has a
best-fit black-body temperature of 150 K, indicating that most of the dust lies
at distances greater than the orbital separation of the spectroscopic binary.
We estimate the radial extent of the dust with a disk model that approximates
radiation from the spectroscopic binary as a single source of equivalent
luminosity. Given the data, the most-likely values of disk properties in the
ranges considered are R_in = 5.0 +/- 2.5 AU, DeltaR = 13+/-8 AU, lambda_0 =
2(+4/-1.5) microns, gamma = 0+/-2.5, and sigma_total = 16+/-3 AU^2, where R_in
is the inner radius, DeltaR is the radial extent of the disk, lambda_0 is the
effective grain size, gamma is the radial power-law exponent of the optical
depth, tau, and sigma_total is the total cross-section of the grains. The range
of implied disk masses is 0.001--0.1 times that of the moon. These results show
that, for a wide range of possible disk properties, a circumbinary disk is far
more likely than a narrow ring.Comment: 11 page Latex manuscript with 3 postscript figures. Accepted for
publication in Astrophysical Journal Letters. Postscript version of complete
paper also available at
http://www.hep.upenn.edu/PORG/web/papers/koerner00a.p
- …